1. Field of the Invention
The present invention relates to a fuel cell, and more particularly to a fuel cell including a plurality of cells each having a three-layer plate assembly and a separator affixed to the plate assembly. The three-layer assembly consists essentially of a solid electrolyte layer, an oxygen electrode affixed to one side of the electrolyte layer and a fuel electrode affixed to the other side of the electrolyte layer. As assembled, each cell forms an intra-cell flow passage and an inter-cell flow passage is formed between each adjacent pair of cells. One of the intra-cell flow passage and the inter-cell flow passage acts as an oxygen-containing gas flow passage for the oxygen electrode while the other acts as a fuel flow passage for the fuel electrode of each cell.
2. Description of the Related Art
FIGS. 19 and 20 show a typically conventional fuel cell. This fuel cell includes a plurality of three-layered structures and separator plates 4 layered one on another alternatively. Each separator plate 4 defines a plurality of laterally extending grooves `m` in one side and a plurality of vertically extending grooves `n` in the other side. One separator 4 and one three-layered structure together form a ceramic cell multi-layered assembly. As a plurality of the cell assemblies are integrated with each other through a sintering process, so that the grooves `m` and the further grooves `n` of the separators 4 form two kinds of flow passages respectively. One kind of these flow passages provide an intra-cell flow passage f1 while the other kind of the flow passages provide an inter-cell flow passage f2 and either of the passages f1 and f2 is used as an oxygen-containing gas flow passage for the oxygen electrode 2 of the cell 6 while the other is used as a fuel flow passage for the fuel electrode 3 of the cell 6. An electrolyte layer 1 is sandwiched between the oxygen electrode 2 and the fuel electrode 3.
In the drawings, marks F1 and F2 denote an air feed passage and an air exhaust passage for the inner-cell flow passages f1. Similarly, further marks F3 and F4 denote an air feed passage and an air exhaust passage for the inter-cell flow passages f2. Numerals 26, 27 denote partition walls for partitioning the air feed passage F1 and the air exhaust passage F2.
According to the above-described conventional construction, the plurality of cells 6 are placed in close contact with each other and are sintered in this condition for the integration, so that the assembly can not compensate for thermal distortion occurring in the plate-like cells 6. So that, cracks tend to occur at the cells 6 and consequently the fuel may leak from the fuel flow passage thereby damaging the entire fuel cell.
According to one conventional attempt to overcome the above problem, there is provided a gap at the region of the inter-cell flow passage f2 between an adjacent pair of plate-like cells 6 each comprising a separator 4 having the intra-cell flow passage f1 affixed to one side (either the side of the oxygen electrode 2 or the fuel electrode 3) of the three-layer plate assembly, so that the gap may effectively absorb the thermal distortion to protect the fuel cell.
One specific construction of the above type is shown in FIGS. 21, 22 and 23. In this construction, an inner space of a casing 20 is partitioned into three regions by means of a pair of parallel partition walls 21, 22. Each of the partition walls 21, 22 has a plurality of parallel extending slit openings 23 for allowing insertion of a cell. Then, the cell 6 is inserted through the slit openings 23 of the two partition walls 21, 22 with opposed openings of the intra-cell flow passage f1 formed by the separator 4 being oriented to face one outer partitioned region 20c and the other outer partitioned region 20a respectively. Then, at the central partitioned region 20b between the adjacent cells 6, there is formed the inter-cell flow passage f2, so that the cells 6 are spaced from each other at this central partitioned region 20b. One side of the central partitioned region 20b relative to the position of the cell provides the air feed passage F3 for each inter-cell flow passage f2 while the other side of the region 20b provides the air exhaust passage F4 for the inter-cell flow passage f2. Also, the outer partition region 20a provides the air exhaust passage F2 for the intra-cell flow passages f1.
The above-described modified construction can indeed avoid the problem of cracks in the cells 6 due to thermal distortion. On the other hand, the assembly has a minimal opening dimension in the direction of the thickness of the cell. Moreover, the assembly requires the formation of the plurality of stages of the slit openings 23 for allowing insertion of the cells with each opening 23 requiring high precision for providing sufficient air-tightness. Furthermore, the plurality of cells 6 must be inserted from one side through the slit openings 23 of the partition walls 21, 22, so that the assembly is very troublesome and costly.
The prior art provides another modified construction, which is shown in FIGS. 24 and 25. In the case of this construction, on each side of the plate-like cell 6, there is provided a first spacer 24 having a thickness substantially equal to and a length longer than the cell 6. Further, on opposed ends of these first spacers 24, there are laid a pair of second spacers 25. Then, on these second spacers 25, there are laid a further cell 6 and further first spacers 24. As these overlaying operations are repeated, between each adjacent cells 6, there is formed an inter-cell flow passage f2 which opposed sides are partitioned by the pair of second spacers 25, so that the adjacent cells 6 are spaced apart from each other at the region of the inter-cell flow passage f2. Further, to four faces of this multi-layer assembly, there are respectively connected an air duct 30 forming an air feed passage F1 for the intra-cell flow passages f1, a further air duct 31 for forming an air exhaust passage F2 for the intra-cell flow passages f1, a still further air duct 28 for forming an air feed passage F3 for the inter-cell flow passages f2 and a still further air duct 29 for forming an air exhaust passage F4 for the inter-cell flow passages f2.
This construction can eliminate the formation of the plurality of slit openings 23. Yet, the construction requires a great number of parts to be assembled with each other, such as the great number of spacers 24, 25 and the four air ducts 28, 29, 30 and 31. Further, it is difficult to connect the air ducts 28, 29, 30, 31 to the multi-layer assembly having the spacers 24, 25 with good air-tightness. Therefore, this construction again suffers the problem of troublesome and costly assembly.